As is well known, the chucks of machining tools are components that are each installed at one end of the main spindle of a machining tool and holds a workpiece, and are classified into general chucks, such as an independent chuck, a universal chuck and a combination chuck, a compressed air chuck, a collet chuck, and a magnetic chuck.
Of these chucks, the magnetic chuck has an advantage in that it enables a workpiece to be attached and fastened thereto without requiring the use of a separate element, but has disadvantages in that it cannot be applied to a workpiece made from non-magnetic material and in that demagnetization must be performed after processing because the workpiece remains magnetized.
Recently, a magnetic chuck, which is formed by combining an AlNiCo magnet having high residual magnetization, and a ferrite (or rare-earth) magnet having very high coercive force and magnetizing force, has been proposed. Such a magnetic chuck has a very excellent workpiece fastening function because it generates a very high magnetic force.
FIGS. 1 and 2 show a conventional magnetic chuck having an AlNiCo magnet and a ferrite (or rare-earth) magnet.
Referring to the drawings, the conventional magnetic chuck 100 includes a chuck main body 110 made of magnetic material and provided with an accommodation hole 110a; an AlNiCo magnet 120 inserted into the accommodation hole 110a of the chuck main body 110; a coil 130 inserted into the accommodation hole 110a of the chuck main body 110 and configured to surround the AlNiCo magnet 120; a first magnetic element 141 inserted into the accommodation hole 110a of the chuck main body 110 and disposed above and adjacent to the AlNiCo magnet 120; and a first ferrite (or rare-earth) magnet 151 inserted into the accommodation hole 110a of the chuck main body 110 and disposed adjacent to the circumferential surface of the first magnetic element 141. Furthermore, the conventional magnetic chuck 100 has a structure in which the elements 120, 130, 141 and 151, inserted into the accommodation hole 110a of the chuck main body 110, are bound together by filling material 100a, and are mounted in the accommodation hole 110a of the chuck main body 110.
The polarity of the AlNiCo magnet 120 is changed according to the direction in which power is supplied through the coil 130.
It is preferred that ferromagnetism material, such as iron, cobalt or nickel, be used for the first magnetic element 141.
The filling material 100a is flowable curing material, that is, insulating material, which allows magnetic force to freely pass therethrough, and is charged into gaps between the chuck main body 110 and the elements 120, 130, 141 and 151, which are inserted into the accommodation hole 110a of the chuck main body 110, thus allowing these elements 120, 130, 141 and 151 to be bound together.
The operation of the conventional magnetic chuck 100 is described with reference to FIGS. 1 and 2 below.
As shown in FIG. 1, when power is applied to the coil 130, and the AlNiCo magnet 120 is thus magnetized, the vertical part 111 of the chuck main body 110, which is adjacent to the first ferrite (or rare-earth) magnet 151, are magnetized to become an S-pole, and the lateral part 112 of the chuck main body 110, which is adjacent to the AlNiCo magnet 120, is magnetized to become an N-pole, so that a closed loop is formed such that a line of magnetic force extends along the direction of the first magnetic element 141→the first ferrite (or rare-earth) magnet 151→the chuck main body 110→the AlNiCo magnet 120→the first magnetic element 141. Accordingly, when the closed loop is formed by the line of magnetic force as shown in FIG. 1, an object 200 to be attached is disposed outside the line of magnetic force that forms the closed-loop, so that the object 200 to be attached is not attached to the magnetic chuck 100 even when the object 200 to be attached, such as a workpiece, is close to or in contact with the top surface of the magnetic chuck 100.
In this state, when power is applied to the coil 130 in a reverse direction, the AlNiCo magnet 120 is inversely magnetized, so that all portions of the magnetic element 141 are changed into an N-pole, and both the vertical part 111 and lateral part 112 of the chuck main body 110 are changed into an S-pole. Accordingly, when the object 200 to be attached, such as a workpiece, is close to the top surface of the magnetic chuck 100, the object 200 to be attached is attached to the vertical part 111 of the chuck main body, which has an S polarity, and the first magnetic element 141, which has an N polarity. When the object 200 to be attached has been attached to the top surface of the magnetic chuck 100 by magnetic force, a closed loop is formed such that a line of magnetic force extends along the direction of the first magnetic element 141→the attached object 200→the chuck main body 110→the AlNiCo magnet 120→the first magnetic element 141.
However, in the conventional magnetic chuck 100, the accommodation hole 110a of the chuck main body 110, in which the individual elements 120, 130, 141 and 151 are mounted, is formed in the form of a depression opened in an upper direction, and the elements 120, 130, 141 and 151 are inserted into the accommodation hole 110a and are laid on the lateral part 112 of the chuck main body 110 to be fixed, so that an object 300 to be attached (refer to FIG. 3) is not attached to the lateral part 112 of the chuck main body 110 even when the object 300 to be attached is close to or in contact with the lateral part 112 of the chuck main body 110.
As described above, the conventional magnetic chuck 100 is problematic in that the availability thereof is low because the object 200 to be attached can be attached only to one surface thereof, the weight of the magnetic chuck 100 itself is heavy due to the lateral part 112 of the chuck main body 110, and the magnetic chuck 100 is thick.